// run: $exec < input
#include <iostream>
#include <vector>
#include <utility>
#include <string>
#include <cmath>

double const r3 = std::sqrt(3);
int n;
std::string s;
double x, y;
typedef std::pair<double, double> pair_type;
std::vector<std::vector<pair_type> > all;

double dis_sqr(pair_type const & a, pair_type const & b)
{
	return (a.first - b.first) * (a.first - b.first) +
		(a.second - b.second) * (a.second - b.second);
}

double const eps = 1e-4;

bool judge(int x)
{
	if (all[x].size() != 3) return false;
	double d1 = dis_sqr(all[x][0], all[x][1]);
	double d2 = dis_sqr(all[x][1], all[x][2]);
	double d3 = dis_sqr(all[x][0], all[x][2]);
	double del1 = std::abs(d1 - d2);
	double del2 = std::abs(d1 - d3);
	return del1 <= eps && del2 <= eps;
}

int main()
{
	while (std::cin >> n && n) {
		std::cin >> s;
		all.clear();
		all.resize(27);
		int t = 0;
		for (int i = 0; i < n; i++) {
			double x = -i / 2.0, y = -i * r3 / 2.0;
			for (int j = 0; j <= i; j++) {
				all[s[t++] - 'a'].push_back(std::make_pair(x, y));
				x += 1;
			}
		}
		std::vector<char> ans;
		for (int i = 0; i < 26; i++)
			if (judge(i)) ans.push_back('a' + i);

		if (!ans.size())
			std::cout << "LOOOOOOOOSER!\n";
		else {
			for (int i = 0; i < (int)ans.size(); i++)
				std::cout << ans[i];
			std::cout << '\n';
		}
	}
}

